Method and system for automatic bond arm alignment

ABSTRACT

A method, as well as a system implementing the method, for automatically aligning a bond arm with respect to a bonding support surface for supporting a substrate during a bonding process. The method comprises: rotating the bond arm for a first revolution around a longitudinal axis through a bond head moveably coupled to the bond arm, the first revolution including a plurality of predefined rotary angular positions; pausing the rotation of the bond arm at each of the plurality of rotary angular positions; determining a tilt angle of the bond arm relative to the bonding support surface during each pause at the respective rotary angular position; and selecting the rotary angular position of the bond arm which has a tilt angle that satisfies a predefined specification such that the bond arm is aligned substantially perpendicular to the bonding support surface.

TECHNICAL FIELD

The present disclosure generally relates to a method and system forautomatic bond arm alignment. More particularly, the present disclosuredescribes various embodiments of a method and a system implementing sucha method for automatically aligning a bond arm with respect to a bondingsupport surface for supporting a substrate during a bonding process.

BACKGROUND

Flip chip bonding is a process for interconnecting semiconductordevices, components, or dies to a circuit board, wafer, or substrate.The semiconductor devices have solder bumps that are deposited on thechip pads on the top surface of the semiconductor devices. Thesemiconductor devices are then flipped over by a flip arm or actuator sothat the top surface faces down, and the chip pads are aligned with thepad surface of the substrate. The bond arm moves to bond thesemiconductor devices onto the substrate, and the solder is reflowed tocomplete the interconnections.

In the flip chip bonding process, control of the tilt angle between thesemiconductor devices and the substrate, i.e. bond arm tilt, iscritical. In an ideal bonding process as shown in FIG. 1A, a bond arm100 actuates or displaces a semiconductor device 20 having solder bumps22 towards a pad surface 32 of a substrate 30, wherein the substrate 30is disposed on an anvil surface or bonding support surface 200 of ananvil or bonding support 202. The solder bumps 22 can bond evenly withthe pad surface 32 and the electrical connections between thesemiconductor device 20 and the pad surface 32 are complete. However, ina non-ideal bonding process as shown in FIG. 1B, the solder bumps 22 donot bond evenly with the pad surface 32. Thus, if the bond arm tilt isnot properly controlled or an acceptable range of bond arm tilt cannotbe achieved, problems such as uneven flatness of the solder bumps 22 asshown in FIG. 1B may occur, increasing the risk of cold joints betweenthe semiconductor device 20 and pad surface 32.

An existing method of controlling bond arm tilt is to manually adjustthe orientation of the bond arm 100 relative to the bonding support 202,specifically the bonding support surface 200. The adjustment may be byway of turning the bond arm 100 about the x-axis and y-axis, such thatthe bond arm 100 points differently towards the bonding support surface200. After adjustment, the bond arm 100 may be mechanically fastened byscrews, and the bond arm tilt can be measured and assessed. Repeatedadjustments may be needed until the measured bond arm tilt satisfies,meets, or complies with a predefined specification. Moreover, thepredefined specification may be tight and fine adjustment of the bondarm tilt may be required after a tool change, e.g. change of a bondcollet.

One problem associated with the existing adjustment method is that therepetitive process of mechanical and manual adjustments followed by thetilting measurement is a qualitative one and is time-consuming. There isalso a risk of human errors, e.g. due to mechanical adjustment in thewrong direction or misreading of measurements.

Therefore, in order to address or alleviate at least one of theaforementioned problems and/or disadvantages, there is a need to providea method and system for automatically aligning a bond arm with respectto a bonding support surface, in which there is at least one improvementand/or advantage over the aforementioned prior art.

SUMMARY

According to a first aspect of the present disclosure, there is a methodfor automatically aligning a bond arm with respect to a bonding supportsurface for supporting a substrate during a bonding process. The methodcomprises: rotating the bond arm for a first revolution around alongitudinal axis through a bond head moveably coupled to the bond arm,the first revolution including a plurality of predefined rotary angularpositions; pausing the rotation of the bond arm at each of the pluralityof rotary angular positions; determining a tilt angle of the bond armrelative to the bonding support surface during each pause at therespective rotary angular position; and selecting the rotary angularposition of the bond arm which has a tilt angle that satisfies apredefined specification such that the bond arm is aligned substantiallyperpendicular to the bonding support surface.

According to a second aspect of the present disclosure, there is asystem for automatically aligning a bond arm with respect to a bondingsupport surface. The system comprises a bonding apparatus for performinga bonding process, comprising: the bond arm; a bond head moveablycoupled to the bond arm; and the bonding support surface for supportingthe substrate during the bonding process; and the system furthercomprises a computing device connected to the bonding apparatus, thecomputing device comprising a processor and a memory configured to storecomputer-readable instructions, wherein when the instructions areexecuted, the processor performs steps comprising: rotating the bond armfor a first revolution around a longitudinal axis through a bond headmoveably coupled to the bond arm, the first revolution including aplurality of predefined rotary angular positions; pausing the rotationof the bond arm at each of the plurality of rotary angular positions;determining a tilt angle of the bond arm relative to the bonding supportsurface during each pause at the respective rotary angular position; andselecting the rotary angular position of the bond arm which has a tiltangle that satisfies a predefined specification such that the bond armis aligned substantially perpendicular to the bonding support surface.

An advantage of one or more of the above aspects of the presentdisclosure is that the alignment of the bond arm can be automaticallyperformed with minimal user intervention. This automatic approach tobond arm alignment or adjustment of a misaligned bond arm significantlyreduces the time required and the flip chip bonding process can becomemore efficient. As user intervention is only required if an acceptablerange of bond arm tilt cannot be found, the trial-and-error approach ofmechanical adjustment such as for every tool change is eliminated orsignificantly reduced. Another advantage is that substantially even bumpflatness can be achieved as the solder bumps can bond evenly with thesubstrate, and the electrical connections between the semiconductordevice and the substrate are complete. Yet another advantage is that therisk of cold joints between the semiconductor device and pad surfaceduring the bonding process is significantly mitigated.

A method and system for automatically aligning a bond arm with respectto a bonding support surface according to the present disclosure arethus disclosed herein. Various features, aspects, and advantages of thepresent disclosure will become more apparent from the following detaileddescription of the embodiments of the present disclosure, by way ofnon-limiting examples only, along with the accompanying drawings inaccordance with embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a side view of a bonding apparatus with an idealrotary angular position.

FIG. 1B illustrates a side view of a bonding apparatus with a non-idealrotary angular position.

FIG. 2A illustrates a side view of a bonding apparatus.

FIG. 2B illustrates a front view of the bonding apparatus of FIG. 2A.

FIG. 3A illustrates a schematic of a bond arm of the bonding apparatusof FIG. 2A with an exaggerated bond arm tilt.

FIG. 3B illustrates a schematic of the bond arm of FIG. 3A which hasbeen aligned by rotation around a longitudinal axis.

FIG. 4A illustrates a flowchart of a method for automatically aligning abond arm with respect to a bonding support surface.

FIG. 4B illustrates a revolution of a bond arm in the method of FIG. 4A.

FIG. 5A illustrates a flowchart of a first selection process of themethod of FIG. 4A.

FIG. 5B illustrates a first revolution of the bond arm in the firstselection process of FIG. 5A.

FIG. 6A illustrates a side view of the bond arm and reference pin of thebonding apparatus of FIG. 2A.

FIG. 6B illustrates a bottom view of a collet surface of the bond arm ofFIG. 6A.

FIG. 6C illustrates a flowchart of determining a tilt angle of the bondarm relative to the bonding support surface from the method of FIG. 4A.

FIG. 7A illustrates a flowchart of a second selection process of themethod of FIG. 4A.

FIG. 7B illustrates a second revolution of the bond arm in the secondselection process of FIG. 7A.

FIG. 8A illustrates a partial revolution of the bond arm of the methodof FIG. 4A.

FIG. 8B illustrates a flowchart of a third selection process after thefirst selection process of FIG. 5A.

FIG. 8C illustrates a flowchart of a third selection process after thesecond selection process of FIG. 7A.

FIG. 8D illustrates a flowchart of another third selection process.

FIG. 9 illustrates a flowchart of the first selection process, secondselection process, and third selection process.

DETAILED DESCRIPTION

In the present disclosure, depiction of a given element or considerationor use of a particular element number in a particular figure or areference thereto in corresponding descriptive material can encompassthe same, an equivalent, or an analogous element or element numberidentified in another figure or descriptive material associatedtherewith. The use of “I” in a figure or associated text is understoodto mean “and/or” unless otherwise indicated. The recitation of aparticular numerical value or value range herein is understood toinclude or be a recitation of an approximate numerical value or valuerange. For purposes of brevity and clarity, descriptions of embodimentsof the present disclosure are directed to a method and system forautomatically aligning a bond arm with respect to a bonding supportsurface, in accordance with the drawings. It will be appreciated thatthe drawings may not be drawn to scale and may not be relied on to showor determine particular sizes and/or dimensions.

While aspects of the present disclosure will be described in conjunctionwith the embodiments provided herein, it will be understood that theyare not intended to limit the present disclosure to these embodiments.On the contrary, the present disclosure is intended to coveralternatives, modifications and equivalents to the embodiments describedherein, which are included within the scope of the present disclosure asdefined by the appended claims. Furthermore, in the following detaileddescription, specific details are set forth in order to provide athorough understanding of the present disclosure. However, it will berecognized by an individual having ordinary skill in the art, i.e. askilled person, that the present disclosure may be practiced withoutspecific details, and/or with multiple details arising from combinationsof aspects of particular embodiments. In a number of instances,well-known systems, methods, procedures, and components have not beendescribed in detail so as to not unnecessarily obscure aspects of theembodiments of the present disclosure.

In representative or exemplary embodiments of the present disclosure,there is a bonding apparatus 10 for performing a flip chip bondingprocess. Referring to FIG. 2A, the bonding apparatus 10 comprises a bondarm or actuator 100 that is moveably coupled to a bond head 102. Acollet 104 is disposed at an end portion of the bond arm 100 for holdingsemiconductor devices or dies. The bonding apparatus 10 furthercomprises an anvil or bonding support 202 with an anvil surface orbonding support surface 200 opposing/facing the collet 104. A referencepin 204 is mounted or fixed to a front track 206 of the bonding support202 for engagement with the collet 104. The reference pin 204 mayalternatively or additionally be mounted or fixed to a rear track 208 ofthe bonding support 202.

The orientation of a rail guiding the bond arm 100 relative to thebonding support surface 200 may be adjusted by moving the bond head 102.For example, the bond head 102 may be turned or rotated about the y-axisto change the orientation of the rail guiding the bond arm 100, which ispointing towards the bonding support surface 200. Referring to FIG. 2B,the bond arm 100 may be turned or rotated about the y-axis byadjustment, i.e. loosening and tightening of the fastening screw 106.The bond arm 100 may also be turned or rotated about the x-axis byadjustment of the fastening screw 108. Accordingly, the bond arm tilt,i.e. the tilt angle α of the bond arm 100 relative to the bondingsupport surface 200, may be varied by adjusting the bond arm 100.Ideally, the tilt angle α is zero or 0° such that the angle α′ betweenthe bond arm 100 and the bonding support surface 200 is exactly 90°,wherein α′=90°−α.

In some embodiments, the bond arm 100 may not be perpendicular to thebond head 102, i.e. the joint angle β between the bond arm 100 and thebond head 102 may not be exactly 90°. For example, FIG. 3A and FIG. 3Bschematically illustrates various exaggerated bond arm tilts of the bondarm 100 relative to the bonding support surface 200, and subsequentalignment of the bond arm 100 relative to the bonding support surface200, respectively. The lower surface 112 of the bond head 102 isparallel to the bonding support surface 200 but the joint angle β is notat 90° to it. There is a longitudinal axis 110 that is perpendicular toand passes through the lower surface 112, specifically at the joint orcoupling between the bond arm 100 and bond head 102. The bond arm 100may be rotated around the longitudinal axis 110 to change the directionof the bond arm 100 pointing towards the bonding support surface 200,such as shown in FIG. 3B wherein the joint angle β is closer to 90° andthe tilt angle α is closer to 0°.

The bond arm 100 is thus rotatable around the longitudinal axis 110through a plurality of rotary angular positions. Some of these rotaryangular positions may result in the tilt angle α being closer to 0° thanother rotary angular positions. In various embodiments with reference tothe flowchart in FIG. 4A and the rotational path or revolution 50 of thebond arm 100 in FIG. 4B, there is a method 300 for automaticallyaligning the bond arm 100 with respect to the bonding support surface200 for supporting a substrate 30 during a bonding process. Broadly, themethod 300 comprises:

-   -   a. a step 302 of rotating the bond arm 100 for a first        revolution 50 around the longitudinal axis 110 through a bond        head 102 moveably coupled to the bond arm 100, the first        revolution 50 including a plurality of predefined rotary angular        positions 40;    -   b. a step 304 of pausing the rotation of the bond arm 100 at        each of the plurality of rotary angular positions 40;    -   c. a step 306 of determining a tilt angle of the bond arm 100        relative to the bonding support surface 200 during each pause at        the respective rotary angular position 40; and    -   d. a step 308 of selecting the rotary angular position 40 which        has a tilt angle that satisfies a predefined specification, such        that the bond arm 100 is aligned substantially perpendicular to        the bonding support surface 200.

If the bond arm 100 is misaligned with respect to the bonding supportsurface 200, the method 300 is performed to align or adjust the bond arm100 until the bond arm 100 is aligned substantially perpendicular to thebonding support surface 200. The alignment of the bond arm 100 withrespect to the bonding support surface 200 is considered to besubstantially perpendicular if the bond arm 100 is rotated to theselected rotary angular position 40 which has a tilt angle thatsatisfies the predefined specification. It will be appreciated that, atthe selected rotary angular position 40, the bond arm 100 may not bealigned exactly perpendicular to the bonding support surface 200.

The bond arm 100 may be manually adjusted until the lower surface 112 isas parallel to the bonding support surface 200 as possible beforeperforming the method 300, but human dexterity and/or manufacturingdefects may limit the degree of parallelism, thereby affecting the tiltangle α of the bond arm 100 relative to the bonding support surface 200.The rotation of the bond arm 100 may be driven by a servomotor orstepper motor or any other mechanism known to the skilled person. Therotary angular positions 40 are predefined and distributed across thefirst revolution 50, i.e. a 360° rotation. The rotary angular positions40 are preferably evenly distributed such that the intervals betweenevery pair of consecutive rotary angular positions 40 are the same. Itwill be appreciated that the number of predefined rotary angularpositions 40 for the first revolution 50 may be different and not evenlydistributed with equal intervals. Further, the angular separationsbetween any pair of consecutive rotary angular positions 40 may also bedifferent, e.g. 90° or 22.5°, and unequal for every distinct pair. Thenumber of iterations of the tilt angle calculation process in the step306 corresponds to the number of rotary angular positions 40.

First Selection Process 400

An embodiment of the method 300 is described with reference to FIG. 5Aand FIG. 5B. The method 300 comprises a first selection process 400 forautomatically aligning the bond arm 100 with respect to the bondingsupport surface 200. The first selection process 400 comprises a step402 of rotating the bond arm 100 for a first revolution 50 a around thelongitudinal axis 110 through the bond head 102 moveably coupled to thebond arm 100, the first revolution 50 a including a plurality ofpredefined rotary angular positions 40. The first revolution 50 a of360° is demarcated into 8 rotary angular positions 40 a-h, such thatevery pair of consecutive rotary angular positions 40 a-h, e.g. between40 a and 40 b or between 40 b and 40 c, are 45° apart. Table 1 belowillustrates the 8 rotary angular positions 40 a-h and the respectiveangular separations from the reference line RL with reference to FIG. 4Band FIG. 5B.

TABLE 1 Rotary Angular Positions in First Selection Process 400 RotaryAngular Separation Angular Position from Reference Line RL 40a 0°/360°40b  45° 40c  90° 40d 135° 40e 180° 40f  225° 40g 270° 40h 315°

The first selection process 400 further comprises a step 404 of pausingthe rotation of the bond arm 100 at each of the plurality of rotaryangular positions 40 a-h, and a step 406 of determining the tilt angle αof the bond arm 100 relative to the bonding support surface 200 duringeach pause at the respective rotary angular position 40 a-h.Particularly, in the step 406, the tilt angles α are determined from atilt angle calculation process 500. In the first revolution 50 a, thebond arm 100 rotates through the 8 rotary angular positions 40 a-h. Ateach of the rotary angular positions 40 a-h, the rotation is paused ortemporarily stopped for performing the tilt angle calculation process500.

Although the bond arm 100 remains stationary immediately before therotation begins and immediately after the rotation ends, thesestationary positions of the bond arm 100 may be construed as pauses inthe step 404. The tilt angle calculation process 500 may be performedfirst at the rotary angular position 40 a corresponding to the angularseparation of 0° at the first pause immediately before the rotationbegins, i.e. before the other 7 rotary angular positions 40 b-h.Alternatively, the tilt angle calculation process 500 may be performedlast at the rotary angular position 40 a corresponding to the angularseparation of 360° at the last pause immediately after the rotationends, i.e. after the other 7 rotary angular positions 40 b-h.

Tilt Angle Calculation Process 500

Referring to FIG. 6A and FIG. 6B, the tilt angle calculation process 500broadly comprises probing heights of three or more distinct points 114on the bond arm 100 with the reference pin 204 arranged perpendicular tothe bonding support surface 200. Particularly, the three or moredistinct points 114 are predefined on a collet surface 116 of the collet104 disposed at the end portion of the bond arm 100. It will beappreciated that at least three distinct points 114 are required inorder to define a plane on the collet surface 116. Preferably, the threeor more distinct points 114 are located at a peripheral region 118 ofthe collet surface 116 used to contact and hold a semiconductor device20. Also, more distinct points 114 on the collet surface 116 will makethe plane definition more accurate in case of deviations on the colletsurface 116.

The tilt angle calculation process 500 further comprises actuating ordisplacing the bond arm 100 relative to the reference pin 204, such thatthe reference pin 204 engages each of the three or more distinct points114 on the collet surface 116. The tilt angle calculation process 500further comprises calculating a planar inclination of the collet surface116 relative to the bonding support surface 200 based on the probedheights of the three or more distinct points 114 on the collet surface116. Ideally, the probed heights of all the three or more distinctpoints 114 are the same, such that the collet surface 116 isperpendicular to the reference pin 204 and parallel to the bondingsupport surface 200. There would be zero planar inclination of thecollet surface 116 relative to the bonding support surface 200. However,if at least one distinct point 114 has a different probed height thanthe others, the planar inclination would not be zero.

An embodiment of the tilt angle calculation process 500 is describedwith additional reference to FIG. 6C. As shown in FIG. 6B, there are 4distinct points 114 a-d predefined on the collet surface 116. The tiltangle calculation process 500 comprises a step 502 of displacing thebond arm 100 along the xy-plane towards the reference pin 204 until thecollet surface 116 is facing, e.g. directly above, the reference pin204. The tilt angle calculation process 500 further comprises a step 504displacing the bond arm 100 along the xy-plane until the first distinctpoint 114 a is directly facing the tip 204 a of the reference pin 204.The tilt angle calculation process 500 further comprises a step 506 ofdisplacing the bond arm 100 along the z-axis until the tip 204 a of thereference pin 204 engages or contacts the first distinct point 114 a.The displacement of the first distinct point 114 a along the z-axis,i.e. the distance moved by the first distinct point 114 a along thez-axis towards the tip 204 a of the reference pin 204, is calculated ina step 508, e.g. by a computing device connected to the bondingapparatus 10. In a subsequent step 510, the probed height of the firstdistinct point 114 a relative to the bonding support surface 200 iscalculated from the displacement of the first distinct point 114 a alongthe z-axis as the height of the reference pin 204 is known. The tiltangle calculation process 500 further comprises a step 512 of displacingthe bond arm 100 in a reverse direction along the z-axis for the samedisplacement calculated in the step 508.

The tilt angle calculation process 500 further comprises a step 514 ofdetermining whether the probed heights for all 4 distinct points 114 a-dhave been calculated. If no, the step 514 proceeds to repeat the steps504, 506, 508, and 510 for each of the remaining distinct points 114a-d. In this example, the steps 504, 506, 508, and 510 are repeated forthe remaining three distinct points 114 b-d.

After all the probed heights for all 4 distinct points 114 a-d have beencalculated, the step 514 proceeds to a step 516 of calculating a planarinclination of the collet surface 114 relative to the bonding supportsurface 200 based on the probed heights of the 4 distinct points 114a-d. The tilt angle α can be calculated in a subsequent step 518 basedon the planar inclination. Ideally, the planar inclination of the colletsurface 116 and the tilt angle α of the bond arm 100 relative to thebonding support surface 200 is zero. The step tilt angle calculationprocess 500 thus calculates the planar inclination of the collet surface116 and the tilt angle α for each of the rotary angular positions 40a-h.

After performing the tilt angle calculation process 500 for all 8 rotaryangular positions 40 a-h, the step 406 proceeds to a step 408 ofdetermining the smallest tilt angle α1 among all the tilt angles α fromall 8 rotary angular positions 40 a-h. The first selection process 400further comprises a step 410 of determining whether the smallest tiltangle α1 satisfies the predefined specification. The predefinedspecification provides a limit to an allowable planar inclination of thecollet surface 116 relative to the bonding support surface 200. Forexample, the predefined specification may be 1 μm/mm, which istranslated to mean a vertical displacement of 1 μm for every 1 mm ofhorizontal displacement. In angular terms, the predefined specificationof 1 μm/mm corresponds to an angle of 0.001 radians or 0.0573°. It willbe appreciated that the predefined specification may vary such asdepending on operational constraints or requirements of the bondingapparatus 10 and/or bonding process.

The smallest tilt angle α1 would satisfy, meet, or comply with thepredefined specification, e.g. 1 μm/mm or 0.0573°, if the value of α1 isnot above 0.0573°. If the smallest tilt angle α1 satisfies thepredefined specification, the step 410 proceeds to a step 412 ofselecting the rotary angular position (from one of 40 a-h) with the tiltangle α corresponding to the smallest tilt angle α1. At this selectedrotary angular position, the bond arm 100 is substantially perpendicularto the bonding support surface 200 such that the predefinedspecification is satisfied. The first selection process 400 may endafter the step 412 and the selected rotary angular position will be usedfor the bonding process. Optionally, the step 412 may proceed to a step414 of performing a third selection process 700 on the selected rotaryangular position.

Conversely, if the smallest tilt angle α1 does not satisfy thepredefined specification, which also means that none of the tilt anglesα from all 8 rotary angular positions 40 a-h satisfies the predefinedspecification. A suitable rotary angular position (from one of 40 a-h)for the bonding process cannot be found from the first selection process400. The step 410 may proceed to a step 416 of performing a secondselection process 600. Alternatively, instead of the second selectionprocess 600, the third selection process 700 may be performed on therotary angular position (one of 40 a-h) with the tilt angle αcorresponding to the smallest tilt angle α1 even though the tilt angle αdoes not satisfy the predefined specification.

Second Selection Process 600

The second selection process 600 is described with reference to FIG. 7Aand FIG. 7B. The second selection process 600 comprises a step 602 ofrotating the bond arm 100 for a second revolution 50 b around thelongitudinal axis 110, the second revolution 50 b including a pluralityof second rotary angular positions 60 that are different from thepredefined rotary angular positions 40 of the first revolution 50 a(also referred to as first rotary angular positions 40). The secondrotary angular positions 60 are defined and distributed across thesecond revolution 50 b, i.e. a 360° rotation, without coinciding withany of the first rotary angular positions 40. Particularly, each secondrotary angular position 60 is substantially in-between or bisects a pairof consecutive first rotary angular positions 40. As shown in FIG. 7B,the second revolution 50 b of 360° is demarcated into 8 second rotaryangular positions 60 a-h, such that every pair of consecutive secondrotary angular positions 60, e.g. between 60 a and 60 b or between 60 band 60 c, are 45° apart. Table 2 below illustrates the 8 second rotaryangular positions 60 a-h and the respective angular separations from thereference line RL with reference to FIG. 7B.

TABLE 2 Second Rotary Angular Positions in Second Selection Process 600Second Rotary Angular Separation Angular Position from Reference Line RL60a 22.5° 60b 67.5° 60c 112.5° 60d 157.5° 60e 202.5° 60f  247.5° 60g292.5° 60h 337.5°

Similarly, it will be appreciated that the second rotary angularpositions 60 may be evenly distributed such that the intervals betweenevery pair of consecutive second rotary angular positions 60 are thesame. It will also be appreciated that the number of predefined secondrotary angular positions 60 for the second revolution 50 b may bedifferent, e.g. 4 or 16, and not evenly distributed with equalintervals. Further, the angular separations between any pair ofconsecutive second rotary angular positions 60 may also be different,e.g. 90° or 22.5°, and unequal for every distinct pair.

The second selection process 600 further comprises a step 604 of pausingthe rotation of the bond arm 100 at each of the plurality of secondrotary angular positions 60 a-h, and a step 606 of determining the tiltangle α of the bond arm 100 relative to the bonding support surface 200during each pause at the respective second rotary angular position 60a-h. Particularly, in the step 606, the tilt angles α are determinedfrom the tilt angle calculation process 500.

After performing the tilt angle calculation process 500 for all 8 secondrotary angular positions 60 a-h, the second selection process 600proceeds to a step 608 of determining the smallest tilt angle α2 amongall the tilt angles α from all 8 second rotary angular positions 60 a-h.The second selection process 600 further comprises a step 610 ofdetermining whether the smallest tilt angle α2 satisfies the predefinedspecification.

If the smallest tilt angle α2 satisfies the predefined specification,the step 610 proceeds to a step 612 of selecting the second rotaryangular position (from one of 60 a-h) with the tilt angle αcorresponding to the smallest tilt angle α2. At this selected rotaryangular position, the bond arm 100 is substantially perpendicular to thebonding support surface 200 such that the predefined specification issatisfied. The second selection process 600 may end after the step 612and the selected rotary angular position will be used for the bondingprocess. Optionally, the step 612 may proceed to a step 614 ofperforming the third selection process 700 on the selected rotaryangular position.

Conversely, if the smallest tilt angle α2 does not satisfy thepredefined specification, which also means that none of the tilt anglesα from all 8 second rotary angular positions 60 a-h satisfies thepredefined specification. A suitable rotary angular position (from oneof 40 a-h and 60 a-h) for the bonding process cannot be found from thefirst selection process 400 and second selection process 600. The step610 may proceed to a step 616 of performing the third selection process700 on the rotary angular position (one of 60 a-h) with the tilt angle αcorresponding to the smallest tilt angle α2, even though the tilt angleα does not satisfy the predefined specification. It will be appreciatedthat if α1 (from the first selection process 400) is smaller than α2(from the second selection process 600), the third selection process 700may instead be performed on the rotary angular position with the tiltangle α corresponding to the smallest tilt angle α1, i.e. one of thefirst rotary angular positions 40 a-h from the first selection process400.

Third Selection Process 700

The third selection process 700 is described with reference to FIG. 8A.As mentioned above, the third selection process 700 may be optionallyperformed in the first selection process 400 and/or the second selectionprocess 600, or performed after the second selection process 600 if asuitable rotary angular position cannot be found. The third selectionprocess 700 seeks to find a more suitable rotary angular position andmay also be referred to as a fine-tuning process. Broadly, the thirdselection process 700 comprises rotating the bond arm 100 across aplurality of third rotary angular positions 70 that are closer togetherwithin a rotary angular range that includes the selected rotary angularposition 40/60. As the third rotary angular positions 70 are closertogether, they may also be referred to as finer rotary angular positions70. Further, the selected rotary angular position 40/60 may be referredto as the previously-selected rotary angular position 40/60, i.e.previously selected from the first selection process 400 or secondselection process 600. The third selection process 700 may optionally beperformed if an optimal rotary angular position cannot be found afterthe first selection process 400 and second selection process 600. Therotary angular position 40/60 with the smallest tilt angle α may bedetermined as a chosen rotary angular position for the third selectionprocess 700. The rotary angular range and the plurality of third rotaryangular positions 70 thereof reside along a rotational path or partialrevolution 50 c around the longitudinal axis 110.

The third selection process 700 further comprises of determining thetilt angle α of the bond arm 100 relative to the bonding support surface200 during each pause at the respective third rotary angular position70. Particularly, the tilt angles α are determined from the tilt anglecalculation process 500. If one of the third rotary angular positions 70has a smaller tilt angle α than the tilt angle α of thepreviously-selected rotary angular position 40/60, the third selectionprocess 700 replaces the previously-selected rotary angular position40/60 with one of the third rotary angular positions 70. Accordingly,one of the third rotary angular positions 70 then becomes the selectedrotary angular position 70. Otherwise, the third selection process 700retains the previously-selected rotary angular position 40/60.

Referring to FIG. 8B, in a first example of the third selection process700 performed in the step 414, the previously-selected rotary angularposition 40 d (135° from the reference line RL) has a tilt angle αcorresponding to the smallest tilt angle α1 that satisfies thepredefined specification. Beginning from the previously-selected rotaryangular position 40 d, the third selection process 700 comprises a step702 of rotating the bond arm 100 for a partial revolution around thelongitudinal axis 110, the partial revolution including a plurality ofthird rotary angular positions 70 that are closer together within arotary angular range that includes the previously-selected rotaryangular position 40 d.

It will be appreciated that the previously-selected rotary angularposition 40 d is substantially in-between or bisects the rotary angularrange and the rotary angular range does not extend towards the vicinityof the adjacent rotary angular positions 40 c and 40 e. It will also beappreciated that as the rotary angular positions 40 for the firstrevolution 50 a are at 45° intervals, the rotary angular range may be±20° from the previously-selected rotary angular position 40 d, i.e.from 115 to 155° relative to the reference line RL.

The rotary angular range may be demarcated into intervals that are fineror smaller than the intervals for the first revolution 50 a. Forexample, the rotary angular range may be demarcated into 5° intervals,resulting in 8 third or finer rotary angular positions 70 a-h (excludingthe previously-selected rotary angular position 40 d). Table 3 belowillustrates the 8 third rotary angular positions 70 a-h and therespective angular separations from the reference line RL.

TABLE 3 Third Rotary Angular Positions in Third Selection Process 700after First Selection Process 400 Third Rotary Angular SeparationAngular Position from Reference Line RL 70a 115° 70b 120° 70c 125° 70d130° 70e 140° 70f  145° 70g 150° 70h 155°

The third selection process 700 further comprises a step 704 of pausingthe rotation of the bond arm 100 at each of the plurality of thirdrotary angular positions 70 a-h, and a step 706 of determining the tiltangle α of the bond arm 100 relative to the bonding support surface 200during each pause at the respective third rotary angular position 70a-h. Particularly, in the step 706, the tilt angles α are determinedfrom the tilt angle calculation process 500.

After performing the tilt angle calculation process 500 for all 8 thirdrotary angular positions 70 a-h, the third selection process 700proceeds to a step 708 of determining the smallest tilt angle α3 amongall the tilt angles α from all 8 third rotary angular positions 70 a-h.The third selection process 700 further comprises a step 710 ofdetermining whether the smallest tilt angle α3 is smaller than thesmallest tilt angle α1 of the previously-selected rotary angularposition 40 d. If yes, the step 710 proceeds to a step 712 of replacingthe previously-selected rotary angular position 40 d with one of thethird rotary angular positions 70 a-h, which has the tilt angle αcorresponding to the smallest tilt angle α3, as the selected rotaryangular position. It will be appreciated that if α1 satisfies thepredefined specification, then α3 which is smaller than α1 alsosatisfies the predefined specification. Thus, at this selected rotaryangular position (one of 70 a-h), the bond arm 100 is also alignedsubstantially perpendicular to the bonding support surface 200.

Conversely, if the step 710 determines that the smallest tilt angle α3is not smaller than the smallest tilt angle α1 of thepreviously-selected rotary angular position 40 d, then the step 710proceeds to a step 714 of retaining the previously-selected rotaryangular position 40 d as the selected rotary angular position.

Referring to FIG. 8C, in a second example of the third selection process700 performed in the step 614, the previously-selected rotary angularposition 60 d (157.5° from the reference line RL) has a tilt angle αcorresponding to the smallest tilt angle α2 that satisfies thepredefined specification. Beginning from the previously-selected rotaryangular position 60 d, the third selection process 700 comprises a step702 of rotating the bond arm 100 for a partial revolution around thelongitudinal axis 110, the partial revolution including a plurality ofthird rotary angular positions 70 a-h that are closer together within arotary angular range that includes the previously-selected rotaryangular position 60 d.

It will be appreciated that the previously-selected rotary angularposition 60 d is substantially in between or bisects the rotary angularrange and the rotary angular range does not extend towards the vicinityof the adjacent rotary angular positions 60 c and 60 e. However, as thepreviously-selected rotary angular position 60 d is a result of thesecond selection process 600 which is performed after the firstselection process 400, the rotary angular range additionally should notextend towards the vicinity of the nearest first rotary angularpositions, specifically 40 d (135° from the reference line RL) and 40 e(180° from the reference line RL).

As such, the rotary angular range for this second example is narrowerthan for the first example, such as ±10° from the previously-selectedrotary angular position 60 d, i.e. from 147.5 to 167.5° relative to thereference line RL. The rotary angular range may be demarcated intointervals that are finer or smaller than the intervals for the firstexample. The rotary angular range may be demarcated into 2.5° intervals,resulting in 8 third or finer rotary angular positions 70 a-h (excludingthe previously-selected rotary angular position 60 d). Table 4 belowillustrates the 8 third rotary angular positions 70 a-h and therespective angular separations from the reference line RL.

TABLE 4 Third Rotary Angular Positions in Third Selection Process 700after Second Selection Process 600 Third Rotary Angular SeparationAngular Position from Reference Line RL 70a  147.5° 70b 150° 70c  152.5°70d 155° 70e 160° 70f   162.5° 70g 165° 70h  167.5°

The third selection process 700 further comprises a step 704 of pausingthe rotation of the bond arm 100 at each of the plurality of thirdrotary angular positions 70 a-h, and a step 706 of determining the tiltangle α of the bond arm 100 relative to the bonding support surface 200during each pause at the respective third rotary angular position 70a-h. Particularly, in the step 706, the tilt angles α are determinedfrom the tilt angle calculation process 500.

After performing the tilt angle calculation process 500 for all 8 thirdrotary angular positions 70 a-h, the third selection process 700proceeds to a step 708 of determining the smallest tilt angle α3 amongall the tilt angles α from all 8 third rotary angular positions 70 a-h.The third selection process 700 further comprises a step 710 ofdetermining whether the smallest tilt angle α3 is smaller than thesmallest tilt angle α2 of the previously-selected rotary angularposition 60 d. If yes, the step 710 proceeds to a step 712 of replacingthe previously-selected rotary angular position 60 d with one of thethird rotary angular positions 70 a-h, which has the tilt angle αcorresponding to the smallest tilt angle α3, as the selected rotaryangular position. It will be appreciated that if α2 satisfies thepredefined specification, then α3 which is smaller than α2 alsosatisfies the predefined specification. Thus, at this selected rotaryangular position (one of 70 a-h), the bond arm 100 is also alignedsubstantially perpendicular to the bonding support surface 200.

Conversely, if the step 710 determines that the smallest tilt angle α3is not smaller than the smallest tilt angle α2 of thepreviously-selected rotary angular position 60 d, then the step 710proceeds to a step 714 of retaining the previously-selected rotaryangular position 60 d as the selected rotary angular position.

Referring to FIG. 8D, in a third example of the third selection process700 performed in the step 616, the third selection process 700 comprisesa step 701 of determining a chosen rotary angular position 40/60. Asnone of the tilt angles α from all rotary angular positions 40 a-h and60 a-h satisfy the predefined specification, one of these would bedetermined as the chosen rotary angular position 40/60. Notably, one ofthe 8 first rotary angular positions 40 a-h corresponds to the smallesttilt angle α1 and one of the 8 second rotary angular positions 60 a-hcorresponds to the smallest tilt angle α2. For example, the first rotaryangular position 40 d has the smallest tilt angle α1 and the secondrotary angular position 60 d has the smallest tilt angle α2. If α1 issmaller than α2, the step 701 determines the first rotary angularposition 40 d as the chosen rotary angular position 40 d. If α2 issmaller than α1, the step 701 determines the second rotary angularposition 60 d as the chosen rotary angular position 60 d.

Beginning from the chosen rotary angular position, e.g. 40 d or 60 d,the steps 702, 704, and 706 of the third selection process 700 areperformed, as would be readily understood by the skilled person based onthe above examples. The third rotary angular positions 70 reside withinthe rotary angular range that includes the chosen rotary angularposition. After performing the tilt angle calculation process 500 forall the third rotary angular positions 70, the third selection process700 proceeds to a step 708 of determining the smallest tilt angle α3among all the tilt angles α from all the third rotary angular positions70. The third selection process 700 further comprises a step 709 ofdetermining whether the smallest tilt angle α3 satisfies the predefinedspecification. If yes, the step 709 proceeds to a step 711 of selectingthe third rotary angular position 70 with the tilt angle α correspondingto the smallest tilt angle α3 as the selected rotary angular position.

If the smallest tilt angle α3 still does not satisfy the predefinedspecification, this means that a suitable rotary angular position cannotbe found after the first selection process 400, second selection process600, and third selection process 700. The bond arm 100 cannot be alignedsubstantially perpendicular to the bonding support surface 200.Accordingly, the bonding process may not be able to proceed as there isgreater risk of uneven bump flatness, incomplete electrical connections,and/or cold joints. The step 709 proceeds to a step 713 of displaying amessage on a computing device connected to the bonding apparatus 10. Themessage informs a user of the bonding apparatus 10 that a suitablerotary angular position cannot be found for performing the bondingprocess as none of the rotary angular positions 40, 60, and 70 has atilt angle α that satisfies the predefined specification. The user maythen be required to manually adjust the bonding apparatus 10,particularly the bond arm 100 and/or bond head 102, to change theorientation of the bond arm 100 relative to the bonding support surface200, such as described above with reference to FIG. 2B.

Flowchart of First Selection Process 400, Second Selection Process 600,and Third Selection Process 700

The flowchart in FIG. 9 summarizes the method 300 including the firstselection process 400, second selection process 600, and third selectionprocess 700. The method 300 advantageously provides for automaticalignment of the bond arm 100 with respect to the bonding supportsurface 200. Particularly, the bond arm 100 is aligned to a selectedrotary angular position which has a tilt angle α that satisfies thepredefined specification, such that the bond arm 100 is alignedsubstantially perpendicular to the bonding support surface 200. Asmentioned above, FIG. 3A schematically illustrates an exaggerated bondarm tilt of the bond arm 100 relative to the bonding support surface200. At the rotary angular position shown in FIG. 3A, the tilt angle αis larger at around 30°, which does not satisfy the predefinedspecification, and as such the bond arm 100 is not aligned substantiallyperpendicular to the bonding support surface 200. FIG. 3B schematicallyillustrates an exaggerated bond arm tilt of the bond arm 100 afteralignment by the method 300. At the rotary angular position shown inFIG. 3B, the tilt angle α is substantially close to 0° and satisfies thepredefined specification, such that the bond arm 100 is alignedsubstantially perpendicular to the bonding support surface 200.

As the various processes and steps of the method 300 are performedelectronically or via a computing device, the selection of a suitable oroptimal rotary angular position can be automatically performed withminimal user intervention. Actuation and displacement of the variouscomponents of the bonding apparatus 10 for performing the method 300 maybe performed by automated mechanisms and/or robotics as would be knownto the skilled person. This automatic approach to bond arm alignment oradjustment of a misaligned bond arm significantly reduces the timerequired and the bonding process can become more efficient.Particularly, the method 300 is quick with a maximum required time ofless than 10 minutes to pre-set the various parameters of the firstselection process 400, second selection process 600, and/or thirdselection process 700. As user intervention is only required if anacceptable range of bond arm tilt (i.e. satisfying the predefinedspecification) cannot be found, the trial-and-error approach ofmechanical adjustment such as for every tool change is eliminated orsignificantly reduced.

The selected rotary angular position would later be used as the readyposition of the bond arm 100 for performing a flip chip bonding process.Referring back to FIG. 1A, by performing the bonding process at theselected rotary angular position, a semiconductor device 20 held at thecollet surface 116 of the collet 104 at the bond arm 100 can be evenlybonded to a pad surface 32 of a substrate 30 disposed or supported onthe bonding support surface 200. Substantially even bump flatness can beachieved as the solder bumps 22 can bond evenly with the pad surface 32,and the electrical connections between the semiconductor device 20 andthe pad surface 32 are complete. Moreover, the risk of cold jointsbetween the semiconductor device 20 and pad surface 32 during thebonding process is eliminated or at least significantly mitigated.

The selected rotary angular position enables the bond arm 100 to besubstantially perpendicular to the bonding support surface 200, andcorrespondingly the collet surface 116 to be substantially parallel tothe bonding support surface 200. In some embodiments, the collet 104 iscircular and the orientation of the circular collet surface 116 viewedfrom the bonding support surface 200 is not critical as compared to thetilt angle α. The circular collet surface 116 remains substantiallyinvariant when rotated about the centre thereof. However, in some otherembodiments, the collet 104 may have a different shape and the colletsurface 116 is not invariant when rotated about the centre thereof. Forexample, the collet 104 is rectangular and the orientation of therectangular collet surface 116 becomes more critical. In order toperform the bonding process with a rectangular collet 104, at least 2criteria must be satisfied:

-   -   i. Tilt angle α satisfying the predefined specification; and    -   ii. Rectangular collet surface 116 aligned with the bonding        support surface 200.

During rotation of the bond arm 100 around the longitudinal axis 110 tofind a suitable or optimal rotary angular position, the orientation ofthe rectangular collet surface 116 may be changed and become misalignedwith the orientation of the semiconductor device 20 held at the colletsurface 116. It is thus possible that at the selected rotary angularposition, the tilt angle α satisfies the predefined specification butthe rectangular collet surface 116 is misaligned with the orientation ofthe semiconductor device 20. One possible solution would be to use anadditional motor to turn or rotate the rectangular collet 104 to alignwith the orientation of the semiconductor device 20, while maintainingthe position and orientation of the bond arm 100 relative to the bondingsupport surface 200. Accordingly, the bond arm 100 remains stationarywhile the rectangular collet 104 is turned/rotated relative to the bondarm 100.

Another possible solution would be to fix the rectangular collet 104such that the rectangular collet surface 116 always remains aligned withthe orientation of the semiconductor device 20. The method 300 would beperformed after the rectangular collet 104 is fixed relative to the bondarm 100. As such, during the method 300, only the bond arm 100 would bemoved or rotated to find the rotary angular position with the tilt angleα that satisfies the predefined specification, while the rectangularcollet 104 remains aligned with the orientation of the semiconductordevice 20. The rectangular collet 104 may be fixed by means of a lockingmechanism such as a guide pin.

The method 300, including the first selection process 400, secondselection process 700, and third selection process 700 may beimplemented on a system comprising the bonding apparatus 10 and acomputing device connected thereto. The computing device comprises aprocessor and a memory configured to store computer-readableinstructions, wherein when the instructions are executed, the processorperforms various steps of the method 300. Accordingly, the method 300may be referred to as a computerized method 300. The processor mayalternatively be referred to as a central processor unit or CPU that isin communication with memory or memory devices. The memory storesnon-transitory computer-readable instructions operative by the processorto perform various steps of the method 300 according to embodiments ofthe present disclosure. The memory may be referred to in some contextsas computer-readable storage media and/or non-transitorycomputer-readable media. Non-transitory computer-readable media includeall computer-readable media, with the sole exception being a transitorypropagating signal per se.

The computing device may be configured to display messages, e.g. alertsand notifications, to the user. For example, in the step 713, a messageis displayed to inform the user that a suitable rotary angular positioncannot be found for performing the flip chip bonding process. Thecomputing device may also be configured to provide prompts for the userto input a response. For example, the computing device may prompt theuser to decide whether or not to continue with the third selectionprocess 700, such as in the optional steps 414 and 614. It will beappreciated that the computing device may further be configured torequire user input, e.g. selecting Yes/No options, at various stages ofthe method 300, or more specifically various steps of the firstselection process 400, second selection process 600, and third selectionprocess 700.

In the foregoing detailed description, embodiments of the presentdisclosure in relation to a method and system for automatically aligninga bond arm with respect to a bonding support surface are described withreference to the provided figures. The description of the variousembodiments herein is not intended to call out or be limited only tospecific or particular representations of the present disclosure, butmerely to illustrate non-limiting examples of the present disclosure.The present disclosure serves to address at least one of the mentionedproblems and issues associated with the prior art. Although only someembodiments of the present disclosure are disclosed herein, it will beapparent to a person having ordinary skill in the art in view of thisdisclosure that a variety of changes and/or modifications can be made tothe disclosed embodiments without departing from the scope of thepresent disclosure. Therefore, the scope of the disclosure as well asthe scope of the following claims is not limited to embodimentsdescribed herein.

1. A method for automatically aligning a bond arm with respect to abonding support surface for supporting a substrate during a bondingprocess, the method comprising: rotating the bond arm for a firstrevolution around a longitudinal axis through a bond head moveablycoupled to the bond arm, the first revolution including a plurality ofpredefined rotary angular positions; pausing the rotation of the bondarm at each of the plurality of rotary angular positions; determining atilt angle of the bond arm relative to the bonding support surfaceduring each pause at the respective rotary angular position; andselecting the rotary angular position of the bond arm which has a tiltangle that satisfies a predefined specification, such that the bond armis aligned substantially perpendicular to the bonding support surface.2. The method according to claim 1, further comprising performing asecond selection process comprising a step of rotating the bond arm fora second revolution around the longitudinal axis, the second revolutionincluding a plurality of second rotary angular positions that aredifferent from the predefined rotary angular positions of the firstrevolution.
 3. The method according to claim 2, the second selectionprocess further comprising determining the tilt angle of the bond armrelative to the bonding support surface during each pause at therespective second rotary angular position.
 4. The method according toclaim 3, the second selection process further comprising selecting thesecond rotary angular position of the bond arm which has a tilt anglethat satisfies the predefined specification, such that the bond arm isaligned substantially perpendicular to the bonding support surface. 5.The method according to claim 1, further comprising performing a thirdselection process comprising rotating the bond arm across a plurality ofthird rotary angular positions that are closer together within a rotaryangular range that includes the selected rotary angular position.
 6. Themethod according to claim 5, the third selection process furthercomprising determining the tilt angle of the bond arm relative to thebonding support surface during each pause at the respective finer rotaryangular position.
 7. The method according to claim 1, whereindetermining the tilt angle comprises probing heights of three or moredistinct points on a collet surface of the bond arm with a reference pinarranged perpendicular to the bonding support surface.
 8. The methodaccording to claim 7, wherein determining the tilt angle furthercomprises displacing the bond arm relative to the reference pin, suchthat the reference pin engages each of the three or more distinct pointson the collet surface.
 9. The method according to claim 8, whereindetermining the tilt angle further comprises calculating a planarinclination of the collet surface relative to the bonding supportsurface based on the probed heights of the three or more distinct pointson the collet surface.
 10. The method according to claim 9, wherein thepredefined specification provides a limit to an allowable planarinclination of the collet surface relative to the bonding supportsurface.
 11. A system for automatically aligning a bond arm with respectto a bonding support surface, the system comprising: a bonding apparatusfor performing a bonding process, comprising: the bond arm; a bond headmoveably coupled to the bond arm; and the bonding support surface forsupporting a substrate during the bonding process; and the systemfurther comprising: a computing device connected to the bondingapparatus, the computing device comprising a processor and a memoryconfigured to store computer-readable instructions, wherein when theinstructions are executed, the processor performs steps comprising:rotating the bond arm for a first revolution around a longitudinal axisthrough a bond head moveably coupled to the bond arm, the firstrevolution including a plurality of predefined rotary angular positions;pausing the rotation of the bond arm at each of the plurality of rotaryangular positions; determining a tilt angle of the bond arm relative tothe bonding support surface during each pause at the respective rotaryangular position; and selecting the rotary angular position of the bondarm which has a tilt angle that satisfies a predefined specificationsuch that the bond arm is aligned substantially perpendicular to thebonding support surface.